Re: [PATCH v1 1/5] KVM: s390: vsie: Fix region 1 ASCE sanity shadow address checks

Janosch Frank
2020-04-03T13:42:00Z

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On 4/2/20 8:48 PM, David Hildenbrand wrote:
> In case we have a region 1 ASCE, our shadow/g3 address can have any value.
> Unfortunately, (-1UL << 64) is undefined and triggers sometimes,
> rejecting valid shadow addresses when trying to walk our shadow table
> hierarchy.
>
> The result is that the prefix cannot get mapped and will loop basically
> forever trying to map it (-EAGAIN loop).
>
> After all, the broken check is only a sanity check, our table shadowing
> code in kvm_s390_shadow_tables() already checks these conditions, injecting
> proper translation exceptions. Turn it into a WARN_ON_ONCE().
>
> Fixes: 4be130a08420 ("s390/mm: add shadow gmap support")
> Cc: <stable@vger.kernel.org> # v4.8+
> Reported-by: Janosch Frank <frankja@linux.ibm.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>

With the WARN_ON_ONCE fix applied I don't run into stalls or warnings
anymore, so:
Tested-by: Janosch Frank <frankja@linux.ibm.com>

> ---
> arch/s390/mm/gmap.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
> index 2fbece47ef6f..f3dbc5bdde50 100644
> --- a/arch/s390/mm/gmap.c
> +++ b/arch/s390/mm/gmap.c
> @@ -787,14 +787,18 @@ static void gmap_call_notifier(struct gmap *gmap, unsigned long start,
> static inline unsigned long *gmap_table_walk(struct gmap *gmap,
> unsigned long gaddr, int level)
> {
> + const int asce_type = gmap->asce & _ASCE_TYPE_MASK;
> unsigned long *table;
>
> if ((gmap->asce & _ASCE_TYPE_MASK) + 4 < (level * 4))
> return NULL;
> if (gmap_is_shadow(gmap) && gmap->removed)
> return NULL;
> - if (gaddr & (-1UL << (31 + ((gmap->asce & _ASCE_TYPE_MASK) >> 2)*11)))
> +
> + if (WARN_ON_ONCE(asce_type != _ASCE_TYPE_REGION1) &&
> + gaddr & (-1UL << (31 + (asce_type >> 2) * 11)))
> return NULL;
> +
> table = gmap->table;
> switch (gmap->asce & _ASCE_TYPE_MASK) {
> case _ASCE_TYPE_REGION1:
>

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